Catalytic treatment of flashed naphtha and gas oil fraction in sour crude oil



Dec. 16. 1969 J. ENG ETAL Filed Jan. 27, 1967 CATALYTIC TREATMENT OF FLASHED NAPHTHA AND GAS OIL FRACTION IN SOUR CRUDE OIL LIGHT NAPHTHA and GAS FRACTIONAI. DISTILLATION TOWER 14 t-LIGHT GAS on 1s ---L- -HEAvY GAS 01L- REACVTOR- FRACTIONATOR v 2 7 700 soun I BOTTOMS- CRUDE j 5 nun- 1 -I'LL 700 REDUCED CRUDE TO VACUUM TOWER JACKSON, 6N6 JOHN 1. new:

INVENTORS PATENT ATTORNEY United States Patent US. Cl. 208--208 8 Claims ABSTRACT OF THE DISCLOSURE Naphtha and gas oil components of sour crude oil are reduced in mercaptan content by treating flashed fractions of the oil containing these components in a low pressure reactor-fractionator containing treating catalyst in the vapor phase section.

Sweetening processes have become conventional treating steps in the refining of petroleum. A variety of fractions boiling in the range of from about 100-800 F. derived from sour petroleum are treated to remove mercaptans. Distinct fractions such as light naphtha, heavy naphtha, kerosenes, jet fuel, diesel oil and heating oils are sweetened to render them more acceptable in specific end use requirements. The sweetening is usually accomplished by one or more treating steps involving the use of such treating agents as chemicals, adsorbents, catalysts and hydrogen. The sweetening treatment can be carried out at any stage in the refining process.

The process of this invention is applied to virgin stocks which have not had any prior refining treatments. One of the principal characteristics of the process is that no hydrogen or other treat gas is employed. Mercaptans are converted to olefins and H 8 by the action of the catalyst on the oil. Catalytic treating of naphtha to remove mercaptans is disclosed in US. Patent 2,740,747 to Sweetser et a1. issued Apr. 3, 1956. Catalytic treating of heating oils to remove mercaptans is disclosed by US. Patent 2,724,684 to Sweetser et al., issued Nov. 22, 1955. Prior art catalytic treating is carried out on specific narrow boiling range fractions and separate reactors are required for each fraction.

The object of this invention is to sweeten the entire naphtha-gas oil fraction of a full boiling range sour crude oil.

Generally speaking the object of the invention is accomplished by treating a flashed naphtha-gas oil fraction without prior separation in a low pressure react rfractionator containing catalyst in the vapor phase section. Other objects and advantages of the invention will be apparent from the following description which discloses certain nonlimiting embodiments. The drawing comprises a diagrammatic flow sheet of a perferred embodiment.

Referring to the drawing, a full 'boiling range sour petroleum crude oil fraction having a mercaptan number of 1050 is passed by line 1 to heater 2. Heat is supplied to the heater by direct firing, indirect heat exchange or by any other suitable heat source, not shown. The oil is 3,484,366 Patented Dec. 16, 1969 heated sufliciently to provide a vaporized fraction having an end point in the range of 450800 F. and in the broad sense the oil can be heated to 450850 F., preferably 600800 F. in heater 2.

' In this embodiment the oil is heated] to a temperature of 700 to 800 F. The latter temperature range is preferred when the fraction to be treated has an end point about 700 F. and includes light and heavy atmospheric gas oil.

The hot oil is passed into a reactor-fractionator tower designated generally by reference numeral 3. The pressure drop across the coils of furnace is about 50100 p.s.i.g. and this drop is sufiicient to create flashing in the reactorfractionator. The reactor-fractionator pressure is maintained at a low pressure value to enhance flash separation of the crude feed into a vapor phase containing the material which is to be treated and a liquid phase which is not to be treated. The tower is maintained at a pressure of about atmospheric pressure to 50 p.s.i.g., i.e., 0-50 p.s.i.g. Preferably the tower is a vertically elongated vessel of a conventional type. Internally the tower contains one or more beds of catalyst 4 located in the upper section. The lower portion contains a reservoir of liquid reduced crude having an upper surface 5. Conventional heating means 6 is used to maintain the liquid at any desired temperature preferably 700 to 800 F. An entrainment means such as entrainment screen 7 is preferably employed to minimize passage of liquid droplets into the catalyst section by entrainment in the flashing vapor. The hot oil enters the tower at a point above the liquid level 5 and below the entrainment screen. Vapor flashes upward and liquid passes downward in the tower as shown by the arrows.

In the present embodiment a fraction boiling in the range of 100 to 700 F. passes up through the catalyst bed 4 at a bed temperature of about 600 to 700 F. and atmospheric pressure. Mercaptans are converted to olefins and H 5.

The catalysts are conventional. Suitable catalysts include a mixture of a member of the group consisting of Group VI oxides and sulfides with a member of the group consisting of iron, cobalt and nickel oxides and sulfides deposited upon a porous carrier of support material such as alumina, silica alumina, bauxite, kieselguhr, magnesia, zirconia, etc., the preferred catalyst is cobalt molybdate on alumina. The catalyst is fully regenerable. A dual reactor system and regenerator, not shown, can be employed.

The treated vapors are passed by line 9 to fractionation tower 10. A valve 8 can be used to adjust tower pressure. A portion of the vapors, i.e., 10 to are returned as liquid reflux to the top of the reaction section via line 11 containing condenser 12. The reflux stream performs the dual functions of stripping the vapors and washing the catalyst surface. In tower 10 a liquid naphtha and gas fraction containing naphtha boiling in the range of 350" F. is recovered by line 13 and routed to a stabilizer not shown for removing light ends including hydrogen sulphide and to recover the sweetened liquid naphtha. A light gas oil fraction of low mercaptan content boiling in the range of 350550 F. is recovered by line 14 and a heavy gas oil fraction of low mercaptan content boiling in the range of 550700 F. is recovered by line 15. A 700 F.+ bottoms fraction is passed by line 16 to line 17 for mixing with the reduced crude bottoms from tower 4. The 700+ material is then sent to other processing units such as a vacuum tower, not shown.

The process of the invention is demonstrated by the following nonlimiting example.

EXAMPLE 1 The sour crude oil to be treated had the properties set forth below in Table 1.

TABLE l.SOUR BLEND CRUDE API gravity 38.5 Sulfur, wt. percent 0.98 Distillation (15 5 plus Hivac):

5% off, F. 100 10 155 20 240 30 320 40 410 50 500 60 600 70 725 80 855 90 1020 RVP 6.0 Visc., SUS at 100 F 37.1 Mercaptan Nos. on

C /350" P. fraction 23 350/550 35 500/700 32 The sour crude was treated in a reactor fractionator similar to the unit shown in the drawing. The test unit comprised a inch diameter stainless steel pipe about 12 inches long heated by resistance wires. A stainless steel mesh entrainment screen was employed and the feed was heated to about 800 F. and passed into the unit at a point below the entrainment screen in the manner disclosed in the drawing. The 700 F.+ liquid fraction was not continuously removed from the bottom of the unit. Instead a 500 cc. quantity of this material was maintained at about 750 F. to serve as a reboiler. The catalyst was 50 cc. of conventional cobalt molybdate on alumina. Additional treating conditions and the test results are set forth below in Table 2.

TABLE 2.-CATALYTIC TREATING OF SOUR CRUDE IN COMBINED REACTOR-FRAOTIONATOR Treat conditions:

Crude oil injected into column at SOC-825 F. Spgace/ vfiliicity of 700 F. and lighter material through catalyst,

v. v. Atmospheric pressure. Entire column heated to prevent heat loss. Reflux ratio of 1:1.

LV percent Mercaptan on feed N Product Mereaptan Nos.:

C/350 F. VT Naphtha 32 1. 1 350/550 Lt. Gas Oil 20 1 6 550/700 Hvy. Gas Oil 11 1. 5

Untreated Treated Naphtha Octanes: RON+3 cc.TEL 80.1 83.6 MON+3 cc. TEL 78.0 81.0

.4 numbers of less than 2.0. The mercaptan number of the gasoline fractions is reduced to about 1.0 and the mercaptan number of the gas oil fractions is reduced to about 1.5 The light naphtha will have improved lead susceptibility because of reduced sulfur content. Costs are reduced over high pressure operations because less expensive fabrication materials can fully satisfy code requirements. The combination of flashing followed by distillation provides more precise separation between middle distillates and cat cracker feed. Since the process does not require hydrogen it can be used where hydrogen is not available. Since treating solutions are not employed no disposal problem arises.

It is to be understood that the foregoing detailed description and example are given by way of illustration and many alterations may be made therein without departing from the spirit of the invention. This applies particularly to the boiling range and mercaptan content of the feed, the operating conditions and the number and boiling ranges of the product fractions.

What is claimed is:

1. An improved process for the removal of mercaptans from the naphtha and gas oil fractions of a sour crude oil comprising the steps of:

(a) heating the crude oil to a temperature in the range (b) passing the heated crude oil into a low pressure catalytic reactor-fractionator tower having a catalyst bed in the upper portion thereof and a reboiler section in the lower portion thereof, said oil being introduced at a point below said catalyst bed and above said reboiler section to flash the naphtha and gas oil fraction;

(c) passing said flashed naphtha and gas oil fraction upwardly through a bed of catalyst in essentially the vapor phase whereby said mercaptans are converted to olefins and H 5;

((1) passing said fraction overhead to a distillation zone;

(e) passing a portion of said fraction to the top of said reactor-fractionator tower as liquid reflux; and

(f) recovering naphtha and gas oil fractions of reduced mercaptan content from said distillation zone and recovering reduced crude as bottoms from said reactor-fractionator tower.

2. Process according to claim 1 in which the catalyst comprises a mixture of cobalt oxide and molybdenum oxide on alumina.

3. Process according to claim 1 in which the sour crude oil has a mercaptan number of 10-50.

4. Process according to claim 1 in which the said pressure ranges from atmospheric pressure to 50 p.s.i.g.

5. Process according to claim 1 in which said pressure is atmospheric pressure.

6. An improved process for the removal of mercaptans in the naphtha and gas oil fractions of'a sour crude oil comprising the steps of:

(1) heating the full boiling range crude oil to a temperature in the range of 450-850 F.,

(2) passing the heated crude oil into a catalytic reactor-fractionator tower having a catalyst bed in the upper poriton thereof and a liquid oil phase in the lower portion thereof, said oil being introduced at a point below the catalyst bed and above the liquid surface of said oil phase at a tower pressure of less than 50 p.s.i.g.,

(3) flashing the naphtha and gas oil fraction having a vapor end point of 450850 F. and passing said fraction upwardly through said bed of catalyst in essentially the vapor phase whereby mercaptans are converted to olefins and H 8,

(4) passing said fraction overhead directly to a fractional distillation zone,

(5) returning a portion of said fraction to the top of the catalyst bed as liquid reflux,

(6) recovering at least one naphtha fraction of reduced rnercaptan content and at least one gas oil fraction of reduced mercaptan content from said zone, (7) and recovering reduced liquid crude oil having an initial boiling point in the range of 450850 F. as bottoms from said tower. 7. Process according to claim 3 in which the crude oil is heated to a temperature in the range of 700800 F. and the end point of the flashed vapor is about 700 F.

8. Process according to claim 6 in which the mercaptan numbers of the treated fractions are less than 2.0.

6 References Cited UNITED STATES PATENTS 2,325,115 7/1943 Egloff 208-243 2,361,651 10/1944 Proell et a1 208-489 2,487,466 11/1949 Nahin 208-243 DELBERT E. GANTZ, Primary Examiner G. J. CRASANAKIS, Assistant Examiner US. Cl. X.R. 208--243, 244 

